Comparison of in vitro antitumor activity between SB3 (trastuzumab biosimilar, Ontruzant) and Herceptin combined with an antibody for subdomain II of HER2 in HER2-positive cancer cells.

Abstract

e14001 Background: The human epidermal growth factor receptor (HER) family plays a critical role in proliferation and survival of cancer cells. Trastuzumab is a recombinant humanized monoclonal antibody that blocks signaling pathways of HER2 tyrosine kinase receptor via binding to subdomain IV of HER2 extracellular domain. A subdomain II targeting therapeutic antibody (DII antibody, pertuzumab) binds to a different region on the same protein. A combination of the two different antibodies might provide a more effective antitumor activity without binding interference [1] . In this study, we evaluate in vitro antitumor activity of SB3 used in the same manner as Herceptin, in combination with a DII antibody that complements the mechanism of action of trastuzumab. [1] Nahta et al, [CANCER RESEARCH 64, 2343–2346, April 1, 2004]. Methods: Similarity assessment of in vitro antitumor activity between SB3 and Herceptin was performed on HER2-overexpressing breast and gastric cancer cells through analyzing HER2 dimerization, cell proliferation and survival activities, and antibody-dependent cellular cytotoxicity (ADCC) in the presence of a DII antibody. Combination index was calculated to evaluate the synergistic effect. Results: SB3 and Herceptin in combination with a DII antibody, showed similar in vitro inhibition rate for HER2/HER3 heterodimerization. The HER2-overexpressing breast and gastric cancer cells growth inhibition rate was similar whether SB3 or Herceptin was used in combination with a DII antibody. This effect was also shown in apoptosis activity by measuring caspase 3/7 expression. In terms of biological effect via Fc function, cell killing activity was assessed by ADCC assay in the presence of a DII antibody, and non-synergistic effect was shown with both SB3 and Herceptin. Conclusions: This study has concluded that SB3, as a trastuzumab biosimilar, demonstrates highly similar in vitro antitumor activity in experimental conditions when combined with a DII antibody, resulting in enhanced cell growth inhibition and apoptosis activities by inhibiting HER2 dimerization in HER2-positive cancer cells.